Electric Circuits EELE 2312 Chapter 1 Circuit Variables

Electric Circuits (EELE 2312) Chapter 1 Circuit Variables & Circuit Elements Basil Hamed

Circuit Theory Mathematical model that approximates the behavior of an actual electrical system Commonly used to refer to an actual electrical system as well as to the model that represents it Basil Hamed 2

Problem Solving • • • Identify what’s given and what’s to be found Sketch a circuit diagram or other visual model Think of several solution methods and choose one Calculate a solution Use your creativity Test your solution Basil Hamed 3

The SI Units Quantity Basic Unit Symbol meter m Mass kilogram Kg Time second S Electric Current ampere A degree kelvin o. K candela cd Length Temperature Luminous intensity 4

1. 1 Circuit Analysis An Overview Need Design Specifications Concept Circuit Model Ideal Circuit Components Circuit Analysis Physical Prototype 5

1. 2 Voltage, Current, & The Basic Circuit Element The concept of Electric Charge is the basis for understanding all electrical phenomena The Separation The Charge electrical of is bipolar charges effects (+ve expends caused & -ve) by energy. charges Voltage in ismotion the energy depend peron unit thecharge rate ofcreated charge by flow. the Electric Charge exists in discrete quantities Electric Current separation is theofrate charges. of charge flow. -19 (1. 6022× 10 C) Electrical Effects attributed to separation of charges and charges in motion 6

1. 3 The Ideal Basic Circuit Element • Two terminals connected to other circuit components • It is described mathematically in terms of current and/or Voltage • It can not be subdivided 7

Passive Sign Convention Whenever the reference direction for the current in an element is in the direction of the reference voltage drop across the element use a positive sign in any expression that relates the voltage to the current. Otherwise, use a negative sign. 8

1. 4 Power and Energy Power: time rate of expending or absorbing energy 9

1. 4 Power and Energy Working Example i=4 A and ʋ=-10 V P=-(-10)(4)=40 W 10

1. 5 Voltage and Current Sources Electrical Source is a device that is capable of converting nonelectric energy to electric energy and vice versa An Ideal Voltage Source is a circuit element that maintains a prescribed voltage across its terminals regardless of the current flowing in those terminals An Ideal Current Source is a circuit element that maintains a prescribed current through its terminals regardless of the voltage across those terminals 11

1. 5 Voltage and Current Sources Independent Sources An Independent Source establishes a voltage or current in a circuit without relying on voltages or currents elsewhere in the circuit 12

1. 5 Voltage and Current Sources Dependent Sources A dependent Source (Controlled Source) establishes a voltage or current whose value depends on the value of a voltage or a current elsewhere in the circuit μ, ρ, α, and β are multiplying constants Active Elements capable of generating electric energy Passive Elements cannot generate electric energy 13

1. 5 Voltage and Current Sources There are five ideal basic circuit elements: voltage sources, current sources, resistors, inductors, and capacitors 14

1. 5 Voltage and Current Sources Active element is one that models a device capable of generating electric energy. Voltage sources and Current sources are example active circuit elements. Passive elements model physical devices that cannot generate electric energy. Resistors, inductors, and capacitors are examples of passive circuit elements. 15

Example 1. 1 Using the definition of the ideal independent voltage and current sources, state which interconnections in the following figures are permissible and which violate the constraints imposed by the ideal sources Valid Invalid 16

Example 1. 2 Using the definition of the ideal independent and dependent sources, state which interconnections in the following figures are valid and which violate the constraints imposed by the ideal sources Invalid Valid Invalid 17

Electrical Resistance is the capacity of materials to impede the flow of current or, more specifically, the flow of electric charge. The circuit element used to model this behavior is the resistor. 18

Electrical Resistance Ohm’s Law 19

Example 1. 3 In each of the following circuits υ or i is not known. (a) Calculate the value of υ or i, (b) Determine the power dissipated in each resistor. 8 V -20 V 10 A -2 A 20

Example 1. 3 b) The power dissipated in each of the four resistors is 21

Kirchhoff’s Laws Kirchhoff’s Current Law 7 Unknowns The algebraic sum of all currents at any node in a circuit equals zero 22

Kirchhoff’s Laws Kirchhoff’s Voltage Law The algebraic sum of all voltages around any closed path in a circuit equals zero 23

Example 1. 4 Sum the currents at each node in the circuit shown. Note that there is no connection dot (●) in the center of the diagram. 24

Example 1. 5 Sum the voltages around each designated path in the circuit shown. 25

Example 1. 6 Use Kirchhoff’s laws and Ohm’s law to find io in the circuit shown and test the solution for io by verifying that the total power generated equals the total power dissipated. 26

Example 1. 7 The terminal voltage and the terminal current were measured on the device shown in the figure shown and the values are tabulated. (a) construct a circuit model of the device inside the box, (b) using the circuit model, predict the power this device will deliver to a 10 Ω resistor. 27

Analysis of Circuits Containing Dependent Sources 28

Example 1. 8 Use Kirchhoff’s laws and Ohm’s law to find the voltage υo in the circuit shown and test the solution by verifying that the total power developed equals the total power dissipated. 29

End of Chapter One Basil Hamed 30